Approaches developed in the previous year for making resonance assignments in larger proteins have been extended and improved. The new methods are affected to a lesser degree by the large resonance line widths which are approximately proportional to the molecular weight of the protein. A four-dimensional NMR experiment has been developed that dramatically reduces spectral overlap in one of the most crowded regions of the NOE spectrum, now permitting the study of interactions between aliphatic residues in proteins of a substantial size. The new experiments provide access to a large number of parameters, such as 13C and 15N chemical shifts and coupling constants, and comparison with crystallographic data indicates that these parameters contain structurally important information. The new techniques have been applied to the study of the interaction between calmodulin and a 26-residue fragment of myosin light chain kinase. A dramatic change in the relative orientation of the two domains of calmodulin upon complexation with the peptide is observed and the peptide changes from a random coil to an alpha-helical conformation upon complexation. A detailed structural characterization is currently in progress.